Abstracts

Nutrient limitation in freshwater ecosystems - experiences from field studies

Understanding the reasons and effects of nutrient limitation is crucial in the context of eutrophication of freshwater ecosystems. Although different conceptual or analytical methods have been used, most of the numerous studies that have been undertaken focused on different forms of nitrogen (N), phosphorus (P) and the simultaneous measurements of chlorophyll a (Chl-a) and phytoplankton.
Recently, the role of P and N has been the subject of controversial discussion amongst limnologists and other lake restoration scientists. Various theoretical paradigms relating to nutrient limitation have emerged as potential decision support systems for authorities and policy makers.
In our opinion, the differences in site-specific conditions (such as mixing behaviour, depth, catchment characteristics and nutrient loadings in sediments) of freshwater ecosystems play an important role and have to be explicitly taken into account when analysing processes of eutrophication and/or proposed restoration measures in the light of nutrient limitation.
This presentation will outline monitoring data from different fresh- and brackish water ecosystems. It focuses on situations where growth is either N or P limited, depending on the relevant paradigm. Experiences from fieldwork studies are presented and serve as the basis to discuss contrasting paradigms of nutrient limitation.

SS11 – Presentation

Response of modified clays in the control of sediment internal P influenced by suspended particulate matter (SPM) in shallow eutrophic lakes and the effects on benthic macroinvertebrate community.

In this study, field mesocosom experiments were carried out to study the effects of a lanthanum-modified bentonite (LMB) and a thermally-modified calcium-rich attapulgite (TCAP) on sediment internal P control and their influence on benthic macroinvertebrate community strcutures. Furthermore, a laboratory incubation study was carried out to investigate the effects of suspended particulate mattter (SPM) on sediment P control of LMB and TCAP. Field results indicated that LMB and TCAP can initially effectively inhibit P release from sediment within five months when compared with control treatment. However, their efficiency diminished after seven months application. This can be resultant from the gradual enhanced labile P content in sediment as evidenced by the diffusive gradients in thin films (DGT) test results. P fractionation analysis indicated that over time, LMB and TCAP will lose their ability to reduce mobile phosphorus in sediment, but they can surely cause a significant increase of calcium bound and residual phosphorus fractions in sediment. Laboratory incubation confirmed that SPM addition can cause a sharp increase in P flux across sediment-water interface as well as an increase of mobile phosphorus in surface sediment. However, geoengineering materials have not been able to exert reduction in macroinvertebrate communities in treated sediment. This study indicates that an effective dose caculation should take SPM effects into consideration in shallow and turbid lake restoration using geoengineering in long-term management.

SS11 – Presentation

Response of modified clays in the control of sediment internal P influenced by suspended particulate matter (SPM) in shallow eutrophic lakes and the effects on benthic macroinvertebrate community.

In this study, field mesocosom experiments were carried out to study the effects of a lanthanum-modified bentonite (LMB) and a thermally-modified calcium-rich attapulgite (TCAP) on sediment internal P control and their influence on benthic macroinvertebrate community strcutures. Furthermore, a laboratory incubation study was carried out to investigate the effects of suspended particulate mattter (SPM) on sediment P control of LMB and TCAP. Field results indicated that LMB and TCAP can initially effectively inhibit P release from sediment within five months when compared with control treatment. However, their efficiency diminished after seven months application. This can be resultant from the gradual enhanced labile P content in sediment as evidenced by the diffusive gradients in thin films (DGT) test results. P fractionation analysis indicated that over time, LMB and TCAP will lose their ability to reduce mobile phosphorus in sediment, but they can surely cause a significant increase of calcium bound and residual phosphorus fractions in sediment. Laboratory incubation confirmed that SPM addition can cause a sharp increase in P flux across sediment-water interface as well as an increase of mobile phosphorus in surface sediment. However, geoengineering materials have not been able to exert reduction in macroinvertebrate communities in treated sediment. This study indicates that an effective dose caculation should take SPM effects into consideration in shallow and turbid lake restoration using geoengineering in long-term management.

Acidification of the Bohemian Forest lakes caused by sulphate and nitrate deposition between the 1950s and 1980s strongly affected benthic and pelagic assemblages of macroinvertebrates. Lake water acidification peaked in the mid-1980s and, along with substantial decrease in acid deposition, has been reversing since then. Chemical recovery of lakes exhibits typical changes in water chemistry, such as a decrease in concentrations of strong acid anions, base cations and aluminium, followed by an increase in pH, acid neutralising capacity and concentration of dissolved organic carbon. However, continuing adverse effects of aluminium delayed the biological recovery for at least a decade and recent assemblages still suffer from acid stress. First signs of biological recovery included colonisation by vagile species, reappearance of some indigenous or acid-sensitive species and decline in abundances of eurytopic acid-tolerant species. This study focuses on eight natural lakes of glacial origin on the Czech side (5) and the German side (3) of the Bohemian Forest. We compare biological recovery of two types of lakes – four partly recovered low-aluminium lakes and four acidic high-aluminium lakes. The main aim is to explore compositional changes of macroinvertebrate assemblages in response to recent changes in lake water chemistry between 2010 and 2015. We also compare recent species richness of aquatic insects to that observed in 1999–2007.

RS16 – Poster

Planktivorous fish positively select Daphnia bearing advanced embryos

Author:

Jana Zemanová(zemanj04@jcu.cz), University of South Bohemia in České Budějovice, Faculty of Science

Coauthor:

Michal Šorf, Jaroslav Vrba

Planktivorous fish are visually oriented predators with the preference for larger and conspicuous zooplankton prey. Hence, the larger cladoceran species such as Daphnia are one of the most preferred fish prey. Moreover, when preying on daphnids, fish focus on the conspicuous individuals like those with clutches or ephippia. Similarly, embryos in the latest developmental stages should be more visible than those in earlier stages because of developed black-pigmented eye. This assumption was experimentally tested in mesocosm experiment. Our results clearly confirmed that fish selectively forage on the daphnids with embryos in the latest developmental stages in the brood chamber than on those with earlier stages. The cladoceran assemblages exposed to fish predation were mostly composed of smaller-sized females with embryos in the early developmental stages. Hence, fish predation may significantly alter daphnids’ reproduction in this way.

RS04 – Poster

Post-disturbance changes of macroinvertebrate assemblages downstream of a large dam in the Dinaric karst river Dobra (Croatia)

Dinaric Mountains’ rivers represent one of the most important hotspots of the European freshwater biodiversity. However, large dams continue to be built and many more are planned on these rivers, despite the scarce knowledge about the dam impact on aquatic biodiversity in this area. In 2010 a new large dam (52.5 m high) on the karst river Dobra (Croatia) was finished and closed. Temporal changes of macroinvertebrate assemblages were examined at the site located 460 m downstream of the dam in the period before (2007-2008) and after the dam closure (2010-2015). Replicate samples of macroinvertebrates were collected in mosses and on stony substrate using hand net. The new dam caused drastic short term changes in water quality, and permanent changes of temperature and flow regime. Mosses and stony substrate significantly differed in macroinvertebrate assemblages in both, pre- and post-disturbance periods. Dam closure represented the most intensive disturbance event, which caused drastic change of macroinvertebrate assemblage structure in both microhabitat types during the first two post-disturbance years: reduction of density of dominant groups such as Amphipoda, Gastropoda and dominant insects groups (Coleoptera, Ephemeroptera and Trichoptera) as well as the drastic increase of Chironomidae density, followed by density recovery of all previous groups in the second year. Samples from 2015 had the highest similarity with pre-disturbance assemblages for both microhabitat types implying partly recovered macroinvertebrate assemblages five years after dam closure. By comparing pre- and post-disturbance data, this study increases our understanding of basic ecological response to damming.

SS01 – Poster

The role of predators in shaping macroinvertebrate assemblages of the Western Carpathian spring fens

Due to the relative stability of environmental conditions in springs, spring communities have been considered to be at their equilibrium, being structured mainly by biotic interactions. The Western Carpathian spring fens (helocrenes) host very abundant and diverse macrofaunal assemblages, known to be significantly driven by environmental conditions and to a lesser extent also by dispersal limitations but the role of biotic interactions remains totally unexplored. Due to the absence of fish, the main “top-down” control in the spring fens is maintained by macroinvertebrates, especially amphipods and insects (e.g., stoneflies, some dipterans). In this study, we test the effect of macrofaunal predators on species density, richness and equitability in the macrofaunal spring fen assemblages on regional scale. We sampled two different mesohabitat types at 45 sites in spring and autumn and measured relevant environmental variables. Our main hypotheses were that 1) the predators reduce the populations of more abundant prey species by means of non-preferential feeding, thus increasing the species equitability and richness, and 2) that this relationship is stronger at the more stable mesohabitat.
This study was supported by the research project of the Czech Science Foundation (P505/16-03881S).

Global warming and eutrophication are two world widely concerned environmental problems. Methane is the second important greenhouse gas, and lake has been proven as a quite important natural source of methane emission. More methane may emit from eutrophic lake due to the higher organic matter deposition in the lake sediment. Lake Chaohu is a shallow and eutrophic lake in eastern China (N31°25′~31°43′, E117°16′~117°05′), with an area of 770 km2 and a mean depth of 2.7 m, and the northwest bay is the most eutrophic area of this lake. A year-round field study was carried out with 20 sites to examine methane distribution and transportation in this eutrophic lake. Samples from the different water and sediment depth was collected using headspace bottle, and methane content was measured by gas chromatography using a flame ionization detector. The potential methane production in the sediment was examined by an indoor incubation experiment. Methane flux from sediment to the overlying water, and methane emission from surface to the air were calculated. The results indicates that more methane accumulated in the northwestern bay of this lake, and higher methane emission rate was also found at this area. More methane content and the higher potential methane production was also found at northwest bay compared to the sediment from the east area of this lake. All results indicate eutrophication enhancing more methane production and emission from Lake Chaohu.

SS12 – Presentation

Shading and sediment structure modulate the structural and functional resistance and resilience of the sediment microbial community to supra-seasonal drought

Drying of isolated stream sediments is reported to impact structure and metabolism of the microbial community. However, the consequences of a drought in the complex environment of a temperate canopied stream with heterogeneous sediment structure and variable light availability are not known. We assessed the impact of a simulated supra-seasonal summer drought in 16 experimental streams that varied in sediment structure (sorted and patched versus homogeneous non-sorted sediments) and shading (low versus highly shaded). The influence of these factors on community structure, community respiration (CR), and net ecosystem production (NEP) was tested in the course of 6 weeks initial colonization, 6 weeks drying, and 2 weeks after flow resumption. During colonization, low shaded streams developed into net autotrophy while highly shaded remained net heterotrophic. Within hours after flow cessation, CR and NEP decreased to low rates whereby the low shaded streams also turned into net heterotrophy. Drying of the stream bed caused further exponential decrease of the community metabolism to almost zero after 20 days. CR rates during drying depended on shading. Following flow resumption, CR peaked within few hours and declined thereafter to level similar to before drying, while NEP recovered slowly. The degree of NEP recovery depended on shading. Sediment structure affected shift of the periphyton community during drying and recovery but surprisingly had no effect on the metabolism. Findings show that despite shift in community composition metabolic function of sediment biofilm is remarkably resilient towards drying and light availability is major factor for its resistance and resilience.